The present invention relates to a radio transceiver (simplex radio transmitter/receiver) and, more particularly, to an improvement in an antenna switching circuit associated with a radio transceiver.
In a radio transceiver, an arrangement is generally made to selectively connect a transmitter and a receiver to an antenna via an antenna switching circuit which is responsive to a transmission/reception control signal, thereby transmitting or receiving such a radio signal as a frequency modulated signal. The antenna switching circuit associated with the radio transceiver includes a nonlinear diode which, during a receive mode operation of the transceiver, generates spurious emission in response to a large power transmission signal which is delivered from the transmitter. Heretofore, the spurious emission has been removed by disposing in a common transmission/reception path between the antenna and the antenna switching circuit a filter made up of an inductor and a capacitor, e.g. a low pass filter. The problem with the filter scheme for the removal of spurious emission is that when it comes to a receive mode operation the filter entails a decrease in reception sensitivity complementary to an insertion loss attributable thereto.